Problem: The graph of $y = f(x)$ is shown below.

[asy]
unitsize(0.3 cm);

real func(real x) {
  real y;
  if (x >= -3 && x <= 0) {y = -2 - x;}
  if (x >= 0 && x <= 2) {y = sqrt(4 - (x - 2)^2) - 2;}
  if (x >= 2 && x <= 3) {y = 2*(x - 2);}
  return(y);
}

int i, n;

for (i = -8; i <= 8; ++i) {
  draw((i,-8)--(i,8),gray(0.7));
  draw((-8,i)--(8,i),gray(0.7));
}

draw((-8,0)--(8,0),Arrows(6));
draw((0,-8)--(0,8),Arrows(6));

label("$x$", (8,0), E);
label("$y$", (0,8), N);

draw(graph(func,-3,3),red);

label("$y = f(x)$", (4,-3), UnFill);
[/asy]

Which is the graph of $y = f \left( \frac{1 - x}{2} \right)$?

[asy]
unitsize(0.3 cm);

picture[] graf;
int i, n;

real func(real x) {
  real y;
  if (x >= -3 && x <= 0) {y = -2 - x;}
  if (x >= 0 && x <= 2) {y = sqrt(4 - (x - 2)^2) - 2;}
  if (x >= 2 && x <= 3) {y = 2*(x - 2);}
  return(y);
}

real funcb(real x) {
  return(func((1 - x)/2));
}

for (n = 1; n <= 5; ++n) {
  graf[n] = new picture;
  for (i = -8; i <= 8; ++i) {
    draw(graf[n],(i,-8)--(i,8),gray(0.7));
    draw(graf[n],(-8,i)--(8,i),gray(0.7));
  }
  draw(graf[n],(-8,0)--(8,0),Arrows(6));
  draw(graf[n],(0,-8)--(0,8),Arrows(6));

  label(graf[n],"$x$", (8,0), E);
  label(graf[n],"$y$", (0,8), N);
}

draw(graf[1],shift((-1/2,0))*xscale(1/2)*reflect((0,0),(0,1))*graph(func,-3,3),red);
draw(graf[2],graph(funcb,-5,7),red);
draw(graf[3],shift((1,0))*xscale(1/2)*reflect((0,0),(0,1))*graph(func,-3,3),red);
draw(graf[4],shift((1/2,0))*xscale(2)*reflect((0,0),(0,1))*graph(func,-3,3),red);
draw(graf[5],shift((1/2,0))*xscale(1/2)*reflect((0,0),(0,1))*graph(func,-3,3),red);

label(graf[1], "A", (0,-10));
label(graf[2], "B", (0,-10));
label(graf[3], "C", (0,-10));
label(graf[4], "D", (0,-10));
label(graf[5], "E", (0,-10));

add(graf[1]);
add(shift((20,0))*(graf[2]));
add(shift((40,0))*(graf[3]));
add(shift((10,-20))*(graf[4]));
add(shift((30,-20))*(graf[5]));
[/asy]

Enter the letter of the graph of $y = f \left( \frac{1 - x}{2} \right).$
Explanation: The graph of $y = f \left( \frac{1 - x}{2} \right)$ is produced by taking the graph of $y = f(x)$ and reflecting it in the $y$-axis, then stretching it horizontally by a factor of 2, then shifting it to the right by one unit.  The correct graph is $\boxed{\text{B}}.$